Research in our group explores the mechanisms of genome stability and the consequences for cancer, including the biochemical mechanism of repair of cross-links between DNA strands and the DNA polymerases that help cells tolerate DNA damage.
Biochemical Mechanisms of DNA Crosslink Repair
This area of our research examines the biochemical mechanism of repair of cross-links between DNA strands. Chemicals that produce cross-links are particularly destructive to genome function and thus, are widely used in cancer chemotherapy.
Exogenous sources of intra-stand crosslinking chemicals include mitomycin C, nitrogen mustard, cisplatin, and psoralen. Endogenous sources creating crosslinks include metabolites created by lipid peroxidation such as acrolein, crotonaldehyde, malondialdehyde and nitric oxide. These agents are widely used for the treatment of leukemia and solid tumors. However, the mechanism of repair in mammalian cells is not well understood and the nucleotide excision repair (NER) pathway may be highly involved in this process. We study how NER proteins help repair DNA crosslinks.
DAPI stained micronuclei
DNA Polymerase theta (POLQ)
We have also identified and are studying the function of other DNA processing enzymes. We have initially cloned the mammalian gene and identified some of the functions of POLQ. This specialized DNA polymerase is important for the repair of DNA double strand-breaks (DSBs) from many sources including x-rays and cancer chemotherapy drugs.
The image to the left shows micronuclei, products from unrepaired DSBs. The frequency of cells displaying micronuclei is higher in POLQ deficient cells than in normal cells.
REV3L knockout mouse skin epithelium
DNA Polymerase zeta (REV3L & REV7)
DNA polymerase zeta (pol ζ) is exceptionally important for controlling mutagenesis and genetic instability in cells. REV3L is the catalytic subunit of pol ζ, while REV7 (MAD2L2) is considered an accessory subunit.
We have generated mouse models with specific deficiencies in DNA polymerase zeta. These models reveal that the enzyme is critical for maintaining chromosome stability and limiting tumorigenesis. Deletion of Rev3L in p53 mutant mice leads to increased cancer incidence and a shortened lifespan. Further, two distinct REV7-binding sites in REV3L are needed to prevent chromosome breaks and confer resistance to DNA damage.
Section of testis from POLN deficient mouse
DNA Polymerase nu (POLN)
We have discovered POLN as a homologue of POLQ are working to identify its biochemical activities. The POLN gene is predominantly expressed in
testis and encodes protein with strand displacement and damage bypass activity.
The image to the right shows gamma-H2AX foci (green dots, places of DNA damage) induced by x-ray irradiation in spermatid cells lacking POLN.
DNA Helicase HELQ
Agents that cause interstrand DNA crosslinks (ICL) are widely used to treat cancer. Our work found that the DNA helicase HELQ helps defend human cells against ICL- inducing agents, associating with ATR-ATRIP DNA damage signaling and homologous recombination components such as BCDX2 that are sometimes altered in ovarian cancer
In the image, the red jagged line outlined in gray represents an interstrand crosslink. HELQ along with ATR and RAD51 paralogs help cells tolerate such interstrand crosslinks.